1. Field of the Invention
The present invention relates to lamps and, more particularly, to a lamp suitable for use as an illumination lamp for a vehicle such as a head lamp or fog lamp, a signal lamp for a vehicle such as a tail lamp or turn signal lamp, a signal lamp for road traffic, or a signal lamp for railway traffic.
2. Background Art
FIGS. 1 to 3 show conventional lamps of this type. A lamp 90 shown in FIG. 1 basically includes: a light source 91; a revolutional paraboloidal reflector 92; and a lens 93 with a lens cut 93a. A light beam from the light source 91 is reflected by the revolutional paraboloidal reflector 92 to form a parallel light beam. The reflected light beam is diffused properly by the lens cut 93a of the lens 93 to provide a desired light distribution property.
A lamp 80 shown in FIG. 2 includes: a light source 81; a reflector composed of a composite reflecting surface 82; and a lens 83. The composite reflecting surface 82 has a plurality of cylindrical parabolic reflecting surfaces that are arranged to have a parabolic configuration in a vertical cross section taken when the lamp 80 is in a mounted state and have a linear configuration in a horizontal cross section (the state shown in the drawing). The lens 83 has no lens cut so that it is see-through. In the lamp 80, the composite reflecting surface 82 provides the light distribution property by itself.
A lamp 70 shown in FIG. 3 includes: a light source 71; a reflector composed of an ellipsoidal reflecting surface 72 having the light source 71 disposed at a first focal point; an aspheric lens 73; and a shade 74 provided if necessary. The ellipsoidal reflecting surface is composed of a spheroid, a composite ellipsoidal surface, or an ellipsoidal free-form surface. In the arrangement, the aspheric lens 73 projects, under magnification, a light source image formed by converging a light beam at a second focal point to provide an irradiating light beam. The lamp 70 of the type using the ellipsoidal reflecting surface 72 is termed a projector type lamp. The light distribution property is obtained by covering an unwanted portion with the shade 74.
In the lamp 90 shown in FIG. 1, however, the lens cut 93a should be formed to have high optical intensity, so that a significant variation is produced in the thickness of the lens 93. This degrades the transparency of the lens and makes it impossible to provide an appearance with enhanced clarity and sense of depth, which is currently preferred on the market.
It is possible to impart an appearance with enhanced clarity to the lamp 80 shown in FIG. 2, since the lens 83 without a lens cut is see-through. However, since the composite reflecting surface 82 positioned at a recessed portion forms a light distribution property, the formation of the light distribution property is limited by such a factor as difficulty in determining the light distribution property in the direction of width.
The lamp 70 shown in FIG. 3 is difficult to mount because of its increased depth dimension. Moreover, the aspheric lens 73 having a small outer diameter leads to a reduced light-emitting area. Therefore, the lamp 70 used as a head lamp is inferior in visibility when viewed from an oncoming vehicle.
Each of the conventional lamps 70, 80, and 90 with the aforesaid structures is generally in wide use. Hence, it is impossible to distinguish them from other items and achieve novelty in terms of design. Furthermore, since the coefficient of use of a luminous flux from the light source is dependent on the depth dimension, the coefficient of use is lowered if the lamp is reduced in thickness.